Fouling of ship hulls by marine organisms has plagued shipping activities for millennia. Fouling presents a significant drag penalty, reducing the efficiency of propulsion and resulting in the expenditure of excess fuel to overcome the drag in order to meet target cruising speed. Fouling also results in the transport of organisms from foreign ecosystems and can result in the introduction of invasive species. Thus, from both an operational and ecological point of view, methods to reduce or eliminate fouling are necessary. Biological fouling of marine organisms on ships has serious consequences for ship performance and mission capability. Fouling results in a rougher surface and an increase in the overall drag of the ship. These may result in increasing the fuel consumption by as much as 40% and overall voyage cost of up to 77%.
While a number of approaches have been taken to prevent fouling, the most successful approach has been the use of coatings containing biocidal chemicals. Organisms are simply killed and either do not settle or are easily removed. Organo-tin and copper compounds have been in use since the 1970s. Although highly effective at reducing fouling, these biocidal agents have been linked to environmental problems. Release of the compounds from the coatings has led to sediment accumulations of the toxins resulting in harm to non-targeted sea life (e.g., oysters). The International Maritime Organization proposed a ban on new applications of organo-tin coatings starting in 2003 and complete removal of these coatings from all ships by 2008. While organo-tin compounds will initially be replaced by other less toxic biocides, such as copper or organic biocides, coating systems that do not leach any kind of biocidal compounds are desired.
Fouling release (FR) coatings appear to be a leading non-toxic alternative to biocide containing coatings. These are coating systems that do not necessarily prevent the settlement of marine organisms, but permit their easy removal with the application of shear to the surface of the coating. Ideally, the hydrodynamic shear on the hull as a ship reaches cruising velocity would be sufficient to remove fouling organisms. Coatings that are also easily cleaned using a water jet are, however, also desired. The most successful of such coatings to date are based on silicone elastomers. It has been shown that coatings with low modulus and low surface energy can often provide easy release of fouling organisms. Due to their low modulus, however, these coatings are very often easily damaged. In addition, such FR coatings may also suffer from poor adhesion, poor durability, and high cost.